The present invention relates to a bevel edging wheel of the type used for edging of an ophthalmic lens edge. More specifically, the present invention relates to a two-piece bevel edging wheel which can more precisely position the bevel on the peripheral edge of an eyeglass lens.
Eyeglass lenses made of polycarbonate, high index, CR-39, glass and materials like Trivex (PPG tm) are known in the art. In order to finish and make these lenses ready for fitting into the eyeglass frame, it is necessary to bevel edge the outer periphery of the lens to give it the proper cross-section to fit in an eyeglass frame. Typically, this is done by an automatic diamond wheel bevel edging machine which includes a rough cut wheel for cutting out the shape and a bevel edging wheel for providing the final contour. Depending on the lens material being ground, the grinding process occurs differently. For example, the harder the material, the faster the process occurs in grinding; the softer the material, the slower the material is removed and the lesser the effect of the grinding wheel on the lens.
Typically, a lens bevel edging machine will be required to grind every type of lens material available. In the past, when glass and CR-39 were the only lens material being supplied by lens manufacturers, the process was easier to perform. Today, with five lens materials readily available and at least one new lens material being developed each year, the diamond wheel is required to grind varying lens materials on one machine with the same results being required for the placement of the contour of the lens edge.
Both two piece and one piece two-grit bevel edging wheels are well known in the art. Two-piece beveling wheels are beneficial in that bevel geometry of the wheel is more precise and it is easier to define the split of the two fine grits of diamond that are used in the beveling wheel at the apex of the convex bevel groove in the beveling wheel. The two different fine grits of varying size being important to influencing the correct position of the contour of the lens edge. With today""s many different materials, changing the size differential of the two fine grits of diamond on each half of the wheel is not adequate to influence the position of the bevel while affording a lens edge finish that is acceptable in the industry.
Therefore, it is a goal in the art to provide a two-piece bevel edging wheel where each of the two parts of the bevel edging wheel have two different bonding matrices which can influence the position of the lens edge contour without consideration of the type of lens materials and give substantially identical lens edge contours on all types of lens materials.
In accordance with the present invention, there is provided a bevel edging wheel for the edge finishing of an ophthalmic eyeglass lens blank. The lens comprises a hub portion which is adapted for attachment to a rotary power source. The wheel includes an outer circumferential cutting surface having a width. The outer circumferential cutting surface includes an abrasive grit attached thereto an also has a circumferential groove therein for forming an edge contour onto an optical lens. The wheel includes two disc like portions mated at the apex of the xe2x80x9cvxe2x80x9d shaped groove so as to form the peripheral contour of the wheel. Each disc portion of the wheel is manufactured separately and has at least a different bond hardness grade on its circumferential cutting surface.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.